/*  RTTY carrier modem generator by serial programming the si5351a dds ocsilator
  by Alastair GW0AJU
*/
#include <EEPROM.h>
#include <Wire.h>
#include <si5351.h>
Si5351 si5351;
long frequency = 14.060e6;
long freq_display = 0;
long start_freq;
long last_Set;
long IF_LO;
long bfo_freq; 
  
int RTTY_logic=13; // Pin 9 - TTL output of RTTY data signal logic

// rtty data from left shift, the "b0 = (1 * start low)" + "b1 to b5 = (5 bit data)" + " b6 + b7 = (2 * stop high)" = 8bit single byte

// bit zero is the start bit, next five are the RTTY data, followed by bits 6 and 7 for stop bit. 
// 2 bits are used for the stop instead of the 1.5bits, the extra addition to 2bit for a stop bit will  not matter,
// it will only extenduate the data sequence, but still be synchronised by the rtty decoder.


byte info[] = {0x13,0x7F,0x2B,0x57,0x2B,0x57,0x0B,0x23};   // space,letter shift,R,Y,R,Y,carrige return,line feed
unsigned long freq;

void collect_tx_message()   // collect rtty data stream message
{
 byte d;  
 
  for (d=0 ; d<8 ; d++ )  //  d = the number RTTY message + control characters in bytes
      {
       tx_data_message(info[d]);
      }   
}

void  tx_data_message(byte mess)  // decode data stream message and transmit rtty signal
{
  byte p;
  
   for (p=0; p<8 ; p++, mess<<1)  // rtty data sent in pattern due to data sequence
            { 
              if ((mess & 0x01) == 0x01)  // detect for mark tone
                  {
                 //  Serial.print("1");
                    digitalWrite(RTTY_logic, HIGH);  // TTL RTTY output at pin 13
                    sendFrequency_mark(frequency); // mark carrier freq = (space freq + 170Hz)
                    delay(20);   // delay period of data bit transmission
                  }
                else if ((mess & 0x01) == 0x00)  // detect for space tone
                  {  
                 // Serial.print("0");
                    digitalWrite(RTTY_logic, LOW);   // TTL RTTY output at pin 13
                    sendFrequency_space(frequency); // space carrier freq
                    delay(20);   // delay period of data bit transmission
                  }    
            }     
  // delay period before retransmission of RTTY message
  // TX tone is mark tone as last used for stop bit of 1.5bits
}


//******************* programming si5351a as vfo oscillator ********************

void sendFrequency_mark(unsigned long f)
{ 
   IF_LO = frequency + 170;
   
    if (last_Set != IF_LO)
       {
          si5351.set_freq( IF_LO * 100ULL, SI5351_CLK2);  // rx local oscillator vfo  
          si5351.update_status();
          last_Set = IF_LO; 
       }  
}

void sendFrequency_space(unsigned long f)
{ 
   IF_LO = frequency;
   
    if (last_Set != IF_LO)
       {
          si5351.set_freq( IF_LO * 100ULL, SI5351_CLK2);  // rx local oscillator vfo  
          si5351.update_status();
          last_Set = IF_LO; 
       }  
}

void setup()
{
 // Serial.begin(9600);
// configure arduino data pins for output


  si5351.init(SI5351_CRYSTAL_LOAD_8PF, 0, 0);
  si5351.set_pll(SI5351_PLL_FIXED, SI5351_PLLA);
  si5351.set_pll(SI5351_PLL_FIXED, SI5351_PLLB);
  si5351.drive_strength(SI5351_CLK2, SI5351_DRIVE_2MA);
  si5351.output_enable(SI5351_CLK0, 0);
  si5351.output_enable(SI5351_CLK1, 0);
  si5351.output_enable(SI5351_CLK2, 1);
  // calibration of vfo with digital frequency counter to test 25MHz crystal
  //si5351.set_freq(50000000,  SI5351_CLK2); 
  si5351.update_status();

  digitalWrite(RTTY_logic, HIGH);  // TTL RTTY output at pin 12
  sendFrequency_mark(frequency); // mark freq = (space freq + 170Hz)
}

void transmission()
{ 
  si5351.output_enable(SI5351_CLK2, 1);  // switch on dds output
  si5351.update_status();
  delay(2000);   // two second period of mark tone before data transmission
  collect_tx_message();
  delay(1000);  // end carrier mark tone
  si5351.output_enable(SI5351_CLK2, 0);  // switch off dds output
  si5351.update_status();
  delay(2000);  // two second transmission break before restarting data transmission
}

void loop()
{
   transmission();
}